A well-known process for treating food pieces prior to deep fat frying is to coat the exterior surface of the food pieces with a wet material only, or a wet material and then a dry material. The wet material is frequently called batter and will be called that herein even though the batter may be wholly egg, wholly milk, or a primarily grain flour and water formulation. The dry material is frequently called breading and will be called that herein even though the breading may be grain flour only, cracker meal, bread crumbs, or other primarily grain based formulations.
One problem associated with the process of battering and breading food pieces is that of making the batter adhere to all exterior surfaces of the food piece. Where batter does not adhere, breading will not adhere well, and the resultant finished product with bare spots is considered to be low grade. An example is in the commercial production of battered and breaded onion rings, wherein the batter will bead up on the natural surfaces of the rings rather than form a smooth coating. However, if the rings are first coated with a very thin layer of a grain flour material, the batter will form a much smoother coating and will avoid beading.
A different problem is faced in the preparation of seafood products, especially wherein fish pieces are sawed from frozen blocks, then coated with tempura style batter and immediately deep fat fried. If a usual tempura batter is applied directly onto the raw frozen fish, it has a distressing tendency to loosen or "blow-off" from the fish surface when the product is fried. When the finish fried batter is not well bonded to the fish, much of it can be lost during freezing and packing and the product becomes low grade. Numerous fish processors have found that a thin coating of a grain flour material applied to the frozen fish surfaces, before application of the tempura batter, will greatly improve the finished product quality by improving the bond between the batter and the fish. The exact mechanism of this improvement is not important to this invention. Tempura batter is commonly known in the United States as a heavy batter including leavening which causes a puffing of the batter when fried.
These two examples of applying a thin coating of floury material to food product before the application of batter and breading, or tempura batter, are called pre-dusting. Several other food products are pre-dusted in a like manner, for various reasons. The desired thickness of the pre-dust coating is usually quite thin, and may be as little as one or two flour particles thick, but has heretofore been impossible to produce dependably. Usually, the color and texture of the food piece may be seen through the coating. Clumps of predust material are usually detrimental to the process and are avoided as much as possible. The pre-dust material is usually based on wheat flour, but may contain other ingredients such as corn flour, dried whey, dried egg solids, starches, gums, leavening, seasonings and shortening.
The process of pre-dusting has been in use for years, usually involving machinery which is relatively expensive and is underutilized, or machinery which damages the product, or both. For instance, a standard breading machine with a bottom product-receiving layer and top coating layer is sometimes used, but this type machine cannot deliver a uniform and very thin top coating. In this type machine, an elevated hopper is the source for the top layer. Devices in the hopper discharge a falling curtain of breading through which the product passes while it is being carried by conveyor on a receiving layer of breading. When the falling curtain is adjusted to deposit a uniform top coating on product below, the deposition is always far heavier than is required for pre-dusting, necessitating extra effort to remove the excess. Such extra effort frequently involves flipping the product to remove the excess top cover, and flipping damages product corners and edges. When the falling curtain is adjusted to deliver a thin coating on product below, the curtain becomes very erratic and deposits a spotty layer on the product. It is difficult to modify a standard breading machine to deposit the thin coating desired for predusting, and this type machine is usually quite expensive in the first place.
Another method of pre-dusting involves tumbling the product, mixed with pre-dust material, inside a rotating drum with its axis nearly horizontal. Helical flighting or other projections inside the drum make the product move axially in the drum, and an exit screening device allows the pre-dust material to be returned for recirculation. Again, tumbling damages product corners and edges, usually more so than in a standard breading machine, as mentioned in the preceding paragraph. An additional objection to drum pre-dusting is that the product leaves the drum in a piled up narrow band which must then be separated and spread by hand for further processing. Hand spreading after pre-dusting removes or changes the predust coating in a spotty manner. A drum breader is usually less expensive than a standard breading machine, but the drum damages the product much more.
One object of this invention is to provide a relatively inexpensive means for applying thin top and side cover of pre-dust material to food product pieces. Another object is to apply the pre-dust material without damage to the product. Another object is to insure that the pre-dust coating is of the minimum thickness desired, and is uniform and without pockets or clumps of pre-dust material.